<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <style>
        body {
            background-color: #999;
        }
        
        .container {
            margin: 100px;
            width: 400px;
            height: 500px;
            border: 1px solid #000;
            box-sizing: border-box;
            display: flex;
            justify-content: space-around;
            align-items: center;
        }
        
        .slider {
            width: 160px;
            height: 180px;
            background-color: aliceblue;
        }
        
        .slider-container {
            margin: 30px;
            width: 0;
            height: 0;
            display: flex;
            justify-content: center;
            align-items: center;
        }
        
        .slider-block {
            flex-shrink: 0;
            width: 20px;
            height: 20px;
            border-radius: 50%;
            background-color: #ca8d8d;
            z-index: 1;
            position: relative;
        }
    </style>
</head>

<body>
    <div class="container">
        <div class="slider">
            <div class="slider-container">
                <div class="slider-block"></div>
            </div>
        </div>
    </div>
</body>

</html>